Free radicals have been observed in complex biological systems such as tissues and subcellular fractions over the past 25 years, but because a wealth of data is buried in an unresolved S-shaped immobilized free radical signal, it has not been possible to determine the significance of the changes in free radical content. We plan to characterize these featureless signals by utilizing advanced ESR techniques which will probe the wealth of information buried in the normal ESR signal. This plan is a direct continuation of our work concerning the role of free radical in carcinogenesis. The methods developed should be applicable to broader fields concerning free radicals in enzymes and in irradiation damage, as well as in cancer.